X, cold greeting (3)
I believe the answer is:
chi
'x' is the definition.
(thesaurus)
'cold greeting' is the wordplay.
'cold' becomes 'c' (eg on taps).
'greeting' becomes 'hi' (hi is a kind of greeting).
'c'+'hi'='CHI'
(Other definitions for chi that I've seen before include "Classical character" , "The 22nd letter of Greek alphabet" , "Greek character" , "seen in Greek writing" , "Greek letter; force in Chinese philosophy" .)